1. Field of the Invention
The present invention generally relates to tape tension mechanisms for use in recording and reproducing apparatuses and, more particularly, is directed to a tape tension mechanism provided at a supply reel side of a recording and reproducing apparatus such as a video tape recorder.
2. Description of the Prior Art
In a recording and reproducing apparatus, for example, a video tape recorder (VTR), a magnetic tape is likely distorted since it is transported in close contact to a rotary head drum, so that the transporting magnetic tape is required to be always applied with a constant tension which is a force for pulling the tape back, that is, a backward tension. To this end, a tape tension mechanism for maintaining a constant backward tension is provided.
The tape tension mechanism is provided at the supply reel side. The tape tension mechanism includes a tension pin which contacts with the magnetic tape in a tape loading complete condition wherein the magnetic tape taken out of a tape cassette passes a predetermined path, a tension arm for supporting the tension pin, and a tension spring connected at one end thereof to the tension arm to urge it so that the tension pin is moved in contact with the tape to apply a tension to the tape through the tension pin.
FIG. 1 of the accompanying drawings shows a schematic diagram of an example of the thus constituted tape tension mechanism of a conventional VTR. Referring to FIG. 1, a reference numeral 1 denotes a main part of the VTR. Tape reels 4a and 4b are rotatably accommodated in a cassette casing 3 of a tape cassette 2 used in the VTR. A magnetic tape T is fixed at both ends thereof to the tape reels 4a and 4b and wound around them. The tape T extends from a supply side opening of the cassette casing 3 to a take-up side opening thereof respectively provided at opposite ends of a front face of the cassette casing 3 through a tape take-out opening 5 provided at the front face of the cassette casing 3.
A head drum 6 has a rotary magnetic head and is disposed in correspondence to a supply reel table 7a and a take-up reel table 7b. The tape reels 4a and 4b of the tape cassette casing 3 are mounted on the supply reel table 7a and the take-up reel table 7b, respectively. A brake drum 8 is provided coaxially on the supply reel table 7a.
Tape loading blocks 9a and 9b for performing tape loading are formed by mounting guide rollers 11a, 11b and movable inclined guides 12a, 12b on movable bases 10a, 10b, respectively. Tape guide members are further constituted by an impedance roller 13, a pinch roller 14, a swing guide 15 and a capstan 16.
A tape tension mechanism 17 is disposed between the thus disposed tape guide members, that is, the supply reel table 7a and the impedance roller 13.
The tape tension mechanism 17 is constituted by a tension arm 18 pivotally mounted at one end thereof to a chassis side, a tension pin 19 implanted on the other end of the tension arm 18, a tension spring 20 for urging the tension arm 18 to swing to one direction, e.g., counterclockwise, and a brake band 21. One end of the brake band 21 is fixed to the chassis side and wound around the brake drum 8 mounted on the supply reel table 7a and the other end thereof is engaged with the tension arm 18.
In an initial state before the tape loading, the tension arm 18 of the tape tension mechanism 17 is rotated clockwise by a position regulation member (not shown) and held at a position opposite to the supply reel table 7a, that is, in the condition such that the tension pin 19 is positioned within the tape take-out opening 5 of the cassette casing 3 together with the guide rollers 11a, 11b and the movable inclined guides 12a, 12b of the tape loading blocks 9a, 9b and the pinch roller 14.
When the tape loading is performed, the tape loading guide blocks 9a and 9b are moved forwardly, and the tension arm 18 is released from the initial state and rotated counterclockwise by a tension of the tension spring 20 so that the tension pin 19 is abutted on the magnetic tape T in a tape loading complete condition and an intermediate portion of the brake band 21 is wound on the brake drum 18.
Thus, a tension is applied to the magnetic tape T by the tension pin 19 abutted thereon. In this state, when the tension of the magnetic tape T is increased, the magnetic tape T presses the tension pin 19, so that the tension arm 18 is rotated clockwise to decrease a pressure of the brake band 21 against the brake drum 8.
Thus, a rotation load of the supply reel table 7a and the tape reel 4a rotated integrally therewith is decreased and also a winding angle of the magnetic tape T around the tension pin 19 is decreased, so that the backward tension against the magnetic tape T is decreased. Further, when the tension of the magnetic tape T is decreased, the tension arm 18 is rotated counterclockwise to increase a pressure of the brake band 21 against the brake drum 8, so that the rotational load of the supply reel table 7a and the tape reel 4a is increased and the winding angle of the magnetic tape T around the tension pin 19 is increased to thereby increase the backward tension.
The magnetic tape T is transported so that a tension applied thereto is almost constant during recording and reproducing.
In this manner, the magnetic tape T is transported at a constant speed in a state that the backward tension is applied thereto. A fast forward mode of a VTR or the like is performed mainly by the following two methods. According to one method, a rotational speed of a capstan motor is changed to a state where a backward tension is applied to the magnetic tape in the same mode as a recording/reproducing mode or constant speed transporting mode and the pinch roller is abutted on the capstan through the tape. According to a second method, the pressure of the pinch roller against the capstan through the magnetic tape is released and the magnetic tape is directly wound by a winding reel in the fast forward mode.
In the thus constituted recording/reproducing apparatus, in a case of transporting the magnetic tape in the fast forward mode by the above-described first method, there is no necessity of providing a specific fast forward mechanism and so the construction of the apparatus can be simplified. However, since the magnetic tape is transported at a high speed in which the backward tension is applied thereto, then tension of a tape transporting system against the tape is increased due to the fast forward of the tape, so that problems such as damage to the tape and so on tend to occur. Thus, it is required to improve the accuracy of a tape guide system or the like in order to prevent the damage of the tape and so on.
In the case of transporting a magnetic tape in the fast forward mode in the above-described by the second method, since the magnetic tape is wound directly by the winding reel, a limiter torque of the winding reel is required to be changed as compared with a case of a constant speed tape transporting mode, so that the construction of the apparatus is complicated.